1. Field of the Invention
The present invention relates to a dental adhesive composition that is excellent in bonding properties and will be used to bond such restorative materials for a living dental tissues as metals, organic polymers, and ceramics to the dental tissues.
2. Description of the Prior Art
In the field of dental materials, a variety of materials have been used for restorating carious teeth and missing teeth. Such materials include metals such as gold, silver, platinum, alloy, and amalgam; organic high polymers such as polymethyl methacrylates, polycarbonates, cured products of polyfunctional vinyl monomers, and composite resins comprising such polymers and fillers; ceramics such as porcelain. However, these materials hardly adhere to the living dental tissues. Therefore, dental adhesive compositions containing, as an adhesive component, a compound having polar groups such as a phosphate group, a hydroxyl group, and an acid anhydride group have been proposed to improve adhesion or bonding between inorganic components such as calcium phosphate (e.g., hydroxy apatite) or organic components such as collagen that form the tooth tissues with the restorative materials.
However, the adhesive containing the phosphate group, hydroxyl group, or acid anhydride group as a functional group had a disadvantage that bonding property to the dentine was not observed at all. This is attributed to the fact that dentine is not an object suitable for bonding with the adhesive containing the functional groups because the protein content in the dentine is considerably high in comparison with the enamel and because a number of dentinal tubules filled with body fluid exist in the dentine. Therefore, when the above prior adhesives are used, a pretreatment of the apatite of the tissue with an etching agent such as phosphoric acid was necessary. Such pretreatment, however, is not only troublesome but also has a problem that the treatment hurts teeth. Besides, bond strength between the tissues and restorative materials is insufficient even when the pretreatment was conducted, and long spells of the pretreatment may not be adopted, due to the problem of harming the teeth. Therefore, there was a disadvantage in that a gap occurs between the restorative material and the dentine after a long period of time even if teeth were restored with the prior adhesives containing the polar groups, and in some cases, the restorative material comes off.